(1) Field of the Invention
This invention relates to a method of fabricating a semiconductor device, and more particularly to a method of fabricating a semiconductor device including a step of forming patterns for measuring a superposition error between two-layer patterns in different lithographic processes.
(2) Description of the Related Art
As this type of patterns, there are alignment error measurement patterns. As shown in FIG. 1, x- and y-axis alignment measurement patterns 42 and 43 are disposed around an internal circuit 41 of the semiconductor device. These x- and y-axis alignment measurement patterns are disposed near the Y- and the X-axis, respectively, with the origin at the center of the lens. Each of these alignment measurement patterns has a main and a secondary scale pattern. In a certain pattern formation step, the main (or secondary) scale pattern is provided, and in a subsequent separate pattern formation step the secondary (or main) scale pattern is provided. An alignment error between these two steps is measured. In this way, the parallel movement error of the alignment error at the lens center is measured with reduced influence of the magnification difference. Further, it is possible to reduce the rotation error by arranging a pair of y-axis alignment measurement patterns 43 and a pair of x-axis alignment measurement patterns 42 to locate at the X- and Y-axis direction ends, respectively, of the circuit pattern 41 and obtaining the average values.
As the errors of layer superposition among the individual layers there are image distortion error and magnification error due to the projecting lens, effects of wafer distortion, reticle manufacture error, etc. in addition to the parallel movement and rotation errors which are errors (alignment errors) stemming from the alignment functions provided in the exposure apparatus.
In the prior art alignment error measurement method, the influence other than the alignment errors has not been taken into consideration, and the alignment error at the lens center has been measured with the x- and y-axis alignment error measurement patterns which are distant from the lens center. Therefore, the errors other than the alignment errors are not obtained, and high accuracy superposition of layers cannot be achieved.